Switch



Jan. 5, 1960 Filed June 25, 1956 A. THOMAS ETAL 2,920,250

SWITCH 2 Sheets-Sheet l In verz tons;

Alexander Thomas, Fran/1'1 in .Z. Yorne ,JL', 5 e

Jan. 5, 1960 A. THOMAS ETAL SWITCH 2 Sheets-Sheet 2 Filed June 25, 1956 Ina/en tons,-

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United States Patent SWITCH Alexander Thomas, Weston, and Franklin L. Torney, Jr., Weymouth, Mass., assignors to Tracerlab, Inc., Boston, Mass., a corporation of Massachusetts Application June 25, 1956, Serial No. 593,499

11 Claims. (Cl. 317-144) This invention relates to electrical switches or relays and more particularly to an electrostatic relay which will respond to signals of very low energy.

Electromagnetic relays for opening and closing a circuit may bemade sufliciently sensitive to operate on small currents, but the expense increases and the ruggedness decreases so rapidly with increase in sensitivity that such relays designed to be operated by very small currents or voltages have not been commercially practical on account of high cost and lack of ruggedness. Moreover, electromagnetic relays have inherent inertia effects which limits their usefulness in applications Where fast switching is required.

It is an object of the present invention to provide a commercially practical relay which will control a work circuit, and will respond rapidly to very small signals.

Another object of the invention is to provide a'system for reliably controlling a work circuit with very low voltages, for instance of a few volts. I

Another object of the invention is to provide an electrostatic switch of simple and inexpensive construction of high sensitivity yet sufficiently rugged to be commercially practical.

' A feature of the invention is the use of what has been termed condenser type relays, that is, relays which respond'to variations in potential rather than an electric current and which require for their operation only that amount of energy which is required to change the charge on an extremely small capacitance. Another feature is that the relay is always sensitized for actuation with the expenditure of negligible power, namely, only that consumed by electrical leakage across the insulation between the electrodes of the relay.

In accordance with the invention a pair of stationary electrically conducting elements are symmetrically disposed with respect to an electrically conducting deflective element, such as a loop of fine wire, or a metallized glass fiber, supported in such a way as to have spring restoring characteristics which tend to maintain it in its position of symmetry. The stationary electrodes are connected in the circuit to be controlled and a source of potential is connected between the stationary electrodes and the deflective element in a manner to establish symmetrical equal and opposite electrostatic fields between the stationary electrodes and the deflective element. The deflective element, in the sensitized condition of the relay, is therefore electrically and physically maintained in a position of symmetry between the stationary electrodes, and is capable of deflection against its spring restoring force by a non-symmetrical electrostatic field toward one of the electrodes depending upon the direction of asymmetry. In a preferred embodiment, the deflective element deflects and makes electrical contact with a stationary electrode, or alternatively, it may contact one of two additional elements in its travel toward one or other of the stationary electrodes. The electrostatic field may be rendered non-symmetrical by application of a signal voltage to one or the other of the stationary electrodes, to

the deflective element, or to a probe disposed in the region between the stationary electrode and the deflective element.

The novel features which are characteristic of the invention are set forth with particularity in the appended claims,'but the invention itself together with other objects, features and advantages thereof, will be better understood from the following description taken in connection with the accompanying drawings in which:

Fig. 1 is vertical section of one form of the switch constructed in accordance with the invention;

Fig. 2 is a vertical section of the switch taken along line 2-2 of Fig. 1;

Fig. 3 is an enlarged fragmentary view illustrating the construction of the deflective element of the switch of Figs. 1 and 2;

Fig. 4 is a top view of a modified form of the invention illustrating an alternative arrangement for supporting the deflective element;

Fig. 5 is an enlarged fragmentary elevation view taken along line 5-5 of Fig. 4 illustrating the alternative arrangement for supporting the deflective element;

Fig. 6 is an end view of Fig. 5 illustrating the deflection characteristics of the deflective element;

Figs. 7 and 8 are diagrams of two circuits suitable for use with the switches of Figs. 15;

Fig. 9 is a vertical section of a modification of the switch illustrated in Fig. 1;

Fig. 10 is a vertical section taken along line 10-10 of Fig. 9;

Figs. 11 and 12 are diagrams of two circuits suitable for use with the switch of Figs. 9 and 10;

Fig. 13 is a schematic diagram illustrating a modification of the switch of Figs. 9 and 10 and a suitable circuit for use therewith; and

Fig. 14 is a schematic diagram illustrating another modification of the switch of igs. l5 and a suitable circuit for use therewith.

Referring to the drawings and first to Figs. 1 and 2, a switch is shown which comprises two stationary electrically conducting electrodes 10 and 11 supported within a hollow cylinder 12 formed of a low leakage insulating material such as Teflon, polystyrene, ceramic or glass. Electrodes 10 and 11 are formed with opposed planar surfaces, preferably circular in area, the electrodes being supported on the cylinder 12 such that the opposing planar surfaces of the electrodes are parallel to each other. A movable or deflective element 13 is supported on a conducting member 14, which, in turn, is supported on base plate 15, also formed of low leakage insulating material. Base plate 15 is secured to cylinder 12 by a suitable cement, and member 14 may also be secured to plate 15 with a suitable cement, shown at 14a. Element 13 may be a circular loop of electrically conducting fiber or wire, such as metallized glass or quartz, stainless steel, tungsten, platinum, Phosphor bronze, or other low decrement material, a loop of a diameter of 0.5 cm. and formed of .00010 diameter metallized quartz fiber hav ing been found satisfactory. As can best be seen in Fig. 3, the wire is formed in a circular loop with the free ends of the wire secured, as by soldering at 13a, in a central opening in conducting member 14, which conveniently may be a length of stainless steel hypodermic needle tubing. Loop 13 is positioned equidistant from electrodes 10 and 11 with the plane of the loop parallel to the flat surfaces of the electrodes, the area of the flat surfaces being equal, or slightly larger, than the area of loop 13. The circular configuration gives the element 13 stability in all directions in the plane of the loop, and permits deflection in either direction normal to the plane of the loop.

with a conducting material 16, such as aquadag.

Since the switch is operative in response to electrostatic fields, it is preferable that the electrodes of the relay be electrostatically shielded to prevent actuation of the switch by stray electrostattic fields. To this end, the outer surfaces of cylinder 12' and base plate 15 are coated It will, of course, be, understood that coating 16 should not contact-electrodes 10, 11 and 14, and in the coating process the circular area immediately surrounding each of these electrodes may be masked so as to retain the insulating properties of the supporting cylinder. Stray electrostatic fields might also enter the cylinder 12 through the top and accordingly, it is preferable that the upper end of cylinder 12 also be closed by a cover plate, such as plate 17, also formed of insulating material, on

which may be applied a coating 16 of material. Alternatively, cover plate 17 may be formed entirely of conductive material and electrically connected to the coating material 16 which covers the sidewalls of cylinder 12.

Figs. 4, and 6 illustrate a modification of the switch just described, the modification being in the method of a supporting the deflective element} As in Fig. l, the

switch comprises a cylinder 12' formed of a suitable insulating material in which are supported a pair of electrically conducting electrodes and 11 having parallel opposed planar surfaces. The deflective element .18, again shown as a circular loop, instead'of being supported as shown in Fig. 3 is supported tangentially on a conducting supporting member 19, which, in turn, is insulatingly supported on cylinder 12.. Supporting ,mem-

ber 19 is oriented with respect to the electrodes such that the plane of loop 18 is parallel to the opposing flat surfaces of electrodes 10 and 11 and equidistant therefrom. Loop 18 may be formed of stainless steel, tungsten, platinum, or Phosphor bronze wire, or may be a thin fiber of metallized glass or quartz, and is secured to support 19 with a spot of solder 20 in the case of a wire loop, or a spot of metallized lead borosilicate in the case of the glassor quartz fiber. With the loop mounted in thismanner, it acts to some extent as a torsional member, particularly over that portion I of its periphery in either direction from the point of mounting. In this case the plane of the loop is distorted less than in the construction of Figs. 1-3, the deflection of the loop being in large measure due to the angular displacement of the relatively short section of the fibernear the point of attachmentdue to the twisting couple P. This torsional restoring force for a given material, deflection, loop diameter, and fiber or wire diameter is less than the bending type of restoring force which is operative in the construction of Figs. 1-3. This means that under these given conditions, a switch constructed in accordance with Figs. 4-6 is more sensitive than a switch constructed in accordance with Figs. 1-3. As shown in Fig. 6, the solid line 18represents the rest plane of the loop and the dotted lines indicate that the loop may de flect in either direction therefrom about itspoint of attachment on support 19, with some distortionof the plane of the loop.

For an understanding of the operation of the switch of the invention, reference is made to Fig. 7 where the switch is schematically illustrated as it may be connected in a work circuit. Prior to. the application of a triggering signal, that is, in its sensitized condition, a battery 22 having its negative terminal connected to defiective element 13 and its positive terminal connected to electrodes 10 and 11 establishes equal and opposite electrostatic fields between the loop and the electrodes. It will be understood, however, that the polarity of battery 22 is immaterial inasmuch as reversal thereof merely alters the polarity of the electrodes with respect to the de flective element. A' device D to be operated by the switch,lsuch as an electromagnet relay, a fine wire fuse to activate a desired chemical reaction, or other currentactivated device, is connected in series with electrode 11.

and a resistor 23 may be connected in series with electrode 10. Since no current is drawn while the switch is in its quiescent condition, the relative resistances of device D and resistor 23 are unimportant. Thus, in the quiescent condition, loop 13 is electrically and mechanically balanced equidistantly between electrodes 10 and 11, the initial position of the loop being independent of the voltage of battery 22 and the electrodes 10 and 11 being geometrically symmetrical with respect to the loop.

A triggering signal may be applied to the switch in a number of ways, one of which is schematically shown in Fig. 7 consisting simply of a battery 24 and a normal- Upon the loop making electrical contact with electrode 11, battery 22 is connected across device D causing device D to be operated as desired in response to the triggering signal. The battery 22' may be of any suitable voltage such as 200 volts, sufiicient to supply an adequate quiescent field for the electrostatic relay and adequate current for operation of device D. If deviceD is not a fuse or other one-shot device, upon removal of the triggering signal, that is by opening switch'25, the bending or torsional characteristics of the loop restores the loop to its rest position thereby opening the work circuit. a 1

If either the field voltage of battery 22 or the triggering signal'from battery 24 is insufficient, the loop 13 moves toward electrode 11 without touching it, and-the switch is inoperative. In general, however, the attracting force of electrode 11 for the loop 13 inc'reaseswith diminished loop distance from electrode 11 to a greater extent than does the restoring-force onthe loop due to its bending and torsional characteristics. 'Thenature of theseopposing forces can be used to advantage to promote stable and operating reliabilityyfor example, the dimensions, geometry and electrical conditions can be made such that the shape of the loop is highly distorted just under the desired trigger voltage, the restoring force as a function of the displacement of the loop at this point departing considerably from Hookes law. When such an adjustment is made, high sensitivity can bemaintained with improved geotropic and shock stability.

Battery 24 and a mechanically operated switch 25 for producing a triggering signal are illustrative only, and normally would be replaced by another, device which develops the necessary triggeringsignal- For example,in Fig. 8, the switch and battery are replaced by ionization chamber 30. For reasons of circuit" design, device D is shown connected in series with deflective ele ment 13 to a common return at' ground potential to which the outer electrode of ionization chamber and the negative terminal of battery 28 are also connected. The positive terminal'of batteryv 28 is connected directly to electrode 11, and through resistor 23 to electrode 10, to establish the symmetrical electrostatic fields described earlier. In the absence of nuclear radiation from source S, ionization chamber 30 acts as a negligiblylow. leakage capacitor andthus has no effect on the switch; Ionization chamber 30 is energized from battery, 28, and under the influence of incident nuclear radiation causes flow of ionization current through resistor 23, which maybe of the order of 10 or 10 ohms, developing a voltage across resistor 23 of sufiicient magnitude to cause actuation of the switch. When connected as shown, current flow is in a direction such that electrode '10 becomes less positive than electrode 11, the electrostatic fields between the electrodes-and loop 13-arerendered unsymmetrical, and

element 13 deflects toward and contacts electrode 11. Upon contacting'electrode 11, battery 28 is put in series with device D and suflicient current is drawn to actuate device D. It is important that ionization chamber 30 and resistor 23 be connected to unbalance the electrostatic fields in a direction such that element 13 deflects toward electrode 11, since otherwise, resistor 23 would be put in series with battery 28 and device D and might limit the current to an extent that device D would not be actuated.

While in Fig. 8 the battery 28 is shown as having its negative terminal connected to deflective element 13 and to the outer electrode of ionization chamber 30, it will be understood that the polarity of battery 28 may be reversed, or the connection of ionization chamber 30 reversed, and still yield the necessary signal. In general, however, battery 28 may be of a lower potential if the central electrode of ionization chamber is made positive. It is advantageous from the standpoint of safety to ground the outer electrode of the ionization chamber.

Figs. 9 and 10 illustrate a modification of the switch of Figs. 1 through 5, particularly in the respect in which the electrostatic fields are rendered unsymmetrical. As before, two stationary electrodes 10 and 11 are supported in a cylinder 12 of insulating material and a deflective element 13, which may be of the form shown in either of Figs. 3 or 5, is symmetrically positioned therebetween with the plane of the loop parallel to the opposed planar surfaces of the electrodes. Cylinder 12 is encased in an outer cylinder 31 of conducting material, with openings provided for the electrodes to insure that they are insulated from each other, this outer cylinder being pro vided to afford electrostatic shielding in the same manner as does coating 16 in the embodiment of Fig. 1. One end of the cylinder 12 is closed by base plate 15 formed of insulating material and the other end is also desirably closed by cover plate 17 to keep out dust and prevent air currents in the region of the electrodes. Cover plates 15 and 17 may be coated with a conducting material 16 to provide electrostatic shielding, or in lieu thereof, cover plate 17 may be formed of metal.

In this embodiment, the electrostatic fields are disturbed by application of a voltage signal to probe 32 supported at the end of conductor 33, which, in turn, is insulatingly supported on cylinder 12. The probe 32 is preferably positioned between one'electrode and the rest position of loop 13 and outside the arc of traverse of the loop during deflection; i.e., as the loop deflects toward one or the other of electrodes 10 and 11 it clears probe 32. Fig. 11 illustrates a circuit using the switch thus modified, and includes a battery 35 connected in series with a suitable device D, which establishes suitable electrostatic fields between loop 13 and electrodes 10 and 11. Since the mere presence of probe 32 in the region between loop 13 and electrode 11 disturbs the symmetry of the field, a balancing signal is applied thereto, from battery 36 connected in series with resistor 37, battery 36 being of such potential that the loop is electrically and physically balanced in the rest position'equidistant between electrodes 10 and 11. Battery 3% and normally opened switch 39 are serially connected in parallel with resistor 37, and closing of switch 39 appiies a triggering voltage from battery 38 to the probe 32. The battery is illustrated as applying a negative triggering signal to the probe which would tend to reduce the attractive force of electrode 11 for the loop with the consequence that loop 13 would deflect to and contact electrode 10, thereby connecting battery 35 across device D. Conversely, if the polarity of battery 38 were reversed, asymmetry would result in the other direction and the loop 13 would deflect to electrode 11. It will be noted, however, that actuation of device D will result regardless of the polarity of the signal applied to probe 32.

In the circuit of Fig. 12, two devices D and D are respectively connected to electrodes 10 and 11, either of which may be actuated by the switch depending upon the polarity of the signal applied to probe 32. As in the circuit of Fig. 11, battery 43 is provided to apply a balancing voltage to probe 32 and two batteries 45 and 46 of opposite polarity may be selectively connected to probe 32 by actuation of switch 47. Thus, if a signal of negative polarity is applied to probe 32, loop 13 is attracted to electrode 10 and device D is actuated. On the other hand, if a signal of positive polarity is applied to probe 32, loop 13 is deflected to electrode 11 and device D is operated.

An extension of the modification of Fig. 9 is schematically illustrated in Fig. 13 where two probes 50 and 51, instead of a single probe, are employed to couple the triggering signal to the switch. The two probes are symmetrically positioned with respect to its corresponding electrode and to loop 13 with the consequence that the balancing potential required for the single probe is unnecessary. As in the circuit of Fig. 12, two devices D and D are respectively connected to electrodes 10 and 11 and symmetrical electrostatic fields are established by battery 52. Probes 50 and 51 are connected together through resistor 52 the center tap of which is connected to the positive terminal of battery 52. A triggering signal for the switch is selectively available from batteries 53 and S4, of opposite polarities as shown, by operation of switch 55. If switch 55 is thrown to connect battery 53 in the circuit, probe 50 is made more negative and 51 more positive with the result that loop 13 is deflected to electrode 11 causing actuation of device D On the other hand, if battery 54 is connected in the circuit, the unbalance of the field will be in the opposite direction and device D will be operated.

Another modification of the switch is shown in Fig. 14 and includes two additional elements 63 and 64 which serve as contacts for loop 13 in the closureof external circuit. The switch is otherwise in all respects similar to that of Fig. 1, having electrodes 10 and 11 symmetrically energized from battery 62 and a deflective element 13 symmetrically disposed therebetween. Triggering signals to render the fields unsymmetrical may be applied to either of electrodes 10 or 11, for example, from battery 65 or 67, upon actuation of its corresponding switch 66 or 68. The unbalance of the electrostatic fields causes deflection of the loop 13 in the manner described above, but instead of being deflected to contact electrode ltlor 11, it intercepts either of contacts 63 or 64 to close the external circuit. For example, if switch 66 is closed thereby to apply a negative triggering voltage to electrode 10, loop 13 is attracted toward electrode 11, but before reaching the electrode, it intercepts contact 64 thereby connecting battery 62 in series with D to actuate the latter. Conversely, if a negative signal is applied to electrode 11 by closing switch 68, loop 13 deflects toward electrode 10 and intercepts electrode 63 causing operation of device D It will also be understood that the switch of Fig. 14 may be modified by the addition of either single or double probes, as shown in Figs. 12 and 13, for the application of trigger signals to the switch. It is also Within the contemplation of the invention to substitute for the solid electrodes 10 and 11, electrodes in the form of a wire grid suitably arranged within cylinder 12 to establish the necessary electrostatic field and to serve as contacts for deflective element 13. Other modifications in the form and construction of the various electrodes of the switch will obviously become apparent to ones skilled in the art, and it is to be understood that throughout the descriptions of Figs. 7 through 14, element 13 may be replaced with the deflective element of Fig. 5 without departing from the invention.

Also, while batteries and mechanically operated switches have been illustrated as a source of triggering signals for the switch, it will be understood that this is illustrative only and that many other devices for example, a photomultiplier, an electronic vacuum tube, or

' insulating material, coated or jacketed with a conducting material to provideelectrostatic shielding of the electrodes supported therein. The functions of insulating the electrodes from each other and of affording electrostatic shielding may also be accomplished by forming cylinder 12 of conducting material; e.g., a length of metal tubing, with electrodes 10, 11 and 13 supported on feed through insulators'inserted in suitably located openings in the walls and end plates. If a metal cylinder is used, cover plates 15 and 17, likewise, would beformed of metal.

It will be appreciated that the air contained within cylinder 12 in the illustrated embodiments, will, to a certain extent, damp the movement of deflcctive element 13 thereby adding to the time required for switching to take place after application of the triggering signal. Switching action may be speeded up by evacuating cylinder 12, in which case, of course, an air-tight assembly is necessary. 7

From the foregoing, it will be apparent that applicants have provided an electrostatic switch which is of relatively simple and inexpensive construction, yet very sensitive. The switch remains sensitized with the expenditure of negligible power, since the only power consumed is that lost by electrical leakage across the insulation. Likewise, the energy required to actuate the switch is very small, only a .few'volts being necessary. The capacitance of the planarelectrodes to each other and to the deflective loop is inherently small, in the range between 0.01 and 1.0 mmf., making the time constant short even when very high impedance circuits (e.g., Fig. 8) are used. The extremely light weight of the deflector makes the mechanical time response short, the inertia effects are small, and the switch may be mounted in any position. A

The switch is useful in many applications, particularly wherever the aforementioned inherent advantages are important, such as in a fuse, as a rectifier, or as a switch for a reversible or irreversible memory circuit. The device D referred to throughout the specification may take a variety of forms, and it will also be apparent that the triggering signal may be developed in a variety of ways. Thus, while there have been shown and described certain embodiments of the invention, it is to be understood that the invention is not to be confined to the precise details set forth by way of illustration, as modifications and variations may be made without departing from the spirit of the invention or exceeding the scope of the appended claims. V

What is claimed is: a

1. An electrostatic switch comprising two stationary electrically conducting electrodes, means supporting a deflectable electrically conducting'element symmetrically with respect to said stationary electrodes, said element having a spring restoring characteristic withreference to said support means normally sufficient to maintain said element in said position, means for establishing symmetrical equal and opposite electrostatic fields between each of said stationary electrodes and said element, and means for destroying the symmetry of said electrostatic fields, said element deflecting from its symmetrical position in response to a non-symmetrical electrostatic field against its spring restoring characteristic.

'2. An electrostatic switch comprising two stationary electrically conducting electrodes insulated from each other and having planar surfaces disposed parallel to each other, a loop formed of a thin fiber of conducting material, means supporting said loop insulated from said electrodesand symmetrically therebetween with the plane of theloop .parallel to the planar surfaces of said electrodes, said loop havinga spring restoring characterist c 8 with reference to said supporting means normally sufli cient to maintain said loop in its position of symmetry, means for normally applying symmetrical equal and opposite electrostatic fields between each of said electrodes and said loop, said loop being deflected from its position of symmetry against its spring restoring characteristic in response to said fields being made unsymmetrical.

3. An electrostatic switch comprising two stationary electrically conducting electrodes insulated from each other and having planar surfaces disposed parallel to each other, a loop formed of a thin fiber of conducting material insulated from said electrodes and symmetrically disposed therebetween with the plane of the loop parallel to the planar surfaces of said electrodes, means supporting said loop at a point on its periphery, said loop having a spring restoring characteristic with reference to said support means normally suflicient to maintain said loop in its position of symmetry, means for establishing equal andopposite electrostatic fields between each of said stationary electrodes and said loop, and means for coupling a voltage signal to said switch to destroy the symmetry of said electrostatic fields, said loop being adapted to deflect from its position of symmetry in response to a non-symmetrical electrostatic field against its spring restoring characteristic.

4. An electrostatic switch comprising two stationary electrically conducting electrodes insulated from each other and having planar surfaces disposed parallel to each other, a loop formed of a thin fiber of conducting material insulated from said electrodes and symmetrically disposed therebetween with the plane of the loop parallel to the planar surfaces of said electrodes, means supporting said loop being at a point on its periphery, said loop having a spring restoring characteristic with reference to said support means normally sufficient-to maintain said loop in its position of symmetry, a source of direct voltage having one terminal connected to said loop and the other terminal connected to said electrodes for establishing equal and opposite electrostatic fields between each of said electrodes and said loop, and means for coupling a voltage signal to said switch to destroy the symmetry of said electrostatic fields, said loop being adapted to deflect from its position of symmetry in response to a non-symmetrical electrostatic field against its spring restoring characteristic.

5. Apparatus in accordance withclaim 4 wherein said voltage signal is applied to one of said stationary electrodes, and said loop deflects to make contact with one of said electrodes.

6. Apparatus in accordance withclaim 4 including a probe disposed in the region between said loop and one of said electrodes and insulated therefrom, and means for coupling a voltage signal to said probe to destroy the symmetry of said electrostatic fields, said loop being constructed and arranged to deflect and make contact with one of said electrodes depending upon the direction of asymmetry of said electrostatic fields.

7. Apparatus in accordance with claim 4 including first and second probes respectively disposed in the regions between said loop and'said electrodes and outside thedeflection arc of said loop,'and means for selectively coupling voltage signals of opposite polarities to one or the other of said probes to destroy the symmetry of said electrostatic fields, said loop being constructed and arranged to deflect and make contact withone of said electrodes depending upon the direction of asymmetry of said electrostatic fields.

8. Apparatus in accordance with claim 4 wherein said voltage signal is applied to one of said electrodes, and first and second contacts insulated from said electrodes and saidloop respectively symmetrically disposed be-.

9. In combination, first and second stationary electrically conducting electrodes insulated from each other and having opposed planar surfaces disposed parallel to each other, a loop formed of a thin fiber of conducting material insulated from said electrodes and symmetrically supported therebetween with the plane of said loop parallel to the planar surfaces of said electrodes, means supporting said loop at a point on its periphery, said loop having a spring restoring characteristic with reference to said support means normally sufficient to maintain said loop in its position of symmetry, a two terminal source of direct potential, a current responsive device connected between one terminal of said source and said loop, a direct connection from the other terminal of said source to said first electrode, a high impedance connection between the other terminal of said source and said second electrode, and an ionization chamber connected between said one terminal of said source and said second electrode, the combination of said source, high impedance, and ionization chamber being operative in response to radiation incident on said ionization chamher to destroy the symmetry of said electrostatic fields causing said loop to deflect from its position of symmetry against its spring restoring characteristic to contact said first electrode and connect said source across said current responsive device.

10. An electrostatic switch comprising a hollow mem ber formed of insulating material, two electrically conducting electrodes supported on and within said member and having spaced opposed planar surfaces disposed parallel to each other, a loop formed of a thin fiber of conducting material having an outward filamentary extension, said loop being insulated from said electrodes and symmetrically supported upon said extension between said electrodes with the plane of said loop parallel to the planar surfaces of said electrode, said loop being thereby supported so as to have a spring restoring characteristic furnished by said extension tending to maintain said loop in its position of symmetry, said loop being adapted to be maintained in said position by symmetrical equal and opposite electrostatic fields between each of said electrodes and said loop and to deflect from its position of symmetry against its spring restoring characteristic in response to said fields being made unsymmetrical.

11. An electrostatic switch comprising a hollow cylinder formed of insulating material, two electrically conducting electrodes supported on and within said cylinder and having spaced, opposed, circular, planar electrodes disposed parallel to each other, a circular loop formed of a fiber of electrically conducting material insulated from said electrodes and symmetrically supported therebetween with the plane of said loop parallel to the planar surfaces of said electrodes, means supporting said loop at a point on its periphery, said loop having a spring restoring characteristic with reference to said support means whereby displacements thereof from its position of symmetry tend to torsionally twist said fiber and being of a diameter to contact one or the other of said electrodes when deflected about said point in a direction normal to the plane of the loop, said loop being adapted to be maintained in its position of symmetry by symmetrical equal and opposite electrostatic fields between each of said electrodes and said loop and to deflect from its position of symmetry against its spring restoring characteristics in response to a voltage signal applied to one of said electrodes of a magnitude to destroy the symmetry of said fields.

References Cited in the file of this patent UNITED STATES PATENTS 749,775 La Cour Jan. 19, 1904 1,605,911 Banneitz Nov. 9, 1926 2,419,111 Bostwick Apr. 15, 1947 FOREIGN PATENTS 395,913 Germany May 23, 1924 79,668 Sweden Aug. 15, 1929 

